<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>通用方式</title>
    <script src="js/jquery-3.3.1.min.js"></script>
</head>
<body>
<form autocomplete="off">
    姓名：<input type="text" id="username">
    <span id="uSpan"></span>
    <br>
    密码：<input type="password" id="password">
    <br>
    <input type="submit" value="注册">
</form>
</body>
<script>
    $("#username").blur(function () {
        let username = $("#username").val();
        $.ajax({
            url:"userServlet",
            async:true,
            data:"username="+username,
            type:"post",
            dataType:"text",
            success:function (data) {
                $("#uSpan").html(data);
            },
            error:function () {
                alert("操作失败！！！");
            }
        });
    });
</script>
</html>